The present invention relates to a thin film transistor (TFT) array inspection apparatus for inspecting a TFT array base plate used for a liquid crystal display, organic electroluminescence (EL) display and the like. More specifically, the present invention relates to an apparatus for inspecting a TFT array by measuring a potential state through a secondary electron obtained by irradiating an electron beam.
A scanning beam apparatus scans a charge beam such as an electron beam and ion-beam on a sample two-dimensionally for forming a scan image. Such a scanning beam apparatus includes an electron beam micro-analyzer, scanning electron microscope, X-ray diffractometer, TFT array inspection apparatus, or the like. Such a scanning beam apparatus described above also includes a defect inspection apparatus for inspecting a defect of picture elements by irradiating an electron beam to a liquid panel matrix base plate and measuring signal strength of a secondary electron beam or the like emitted from the base plate (for example, refer to Patent Document 1).
In order to inspect a base plate state for detecting a picture element defect or the like based on the signal strength of the secondary electron beam, it is necessary to calibrate the signal strength. If the signal strength is not calibrated, it is difficult to accurately inspect the base plate state and compare different base plates.
Conventionally, the scanning beam apparatus does not include a device for calibrating the detected signal strength. Instead, the signal strength is obtained with respect to a standard sample, and a comparison is made based on the standard strength.
On the other hand, in the apparatus using the electron beam, an electron gun as a source of the electron beam is calibrated. In a method of calibrating the electron gun, for example, there are a known method in which a grid disposed at a sample position is scanned and observed to obtain a grid image; and a method in which a filament current flowing through a filament of the electron gun, an emission current of an current source of the electron gun, a beam current irradiated from the electron gun, or the like, is measured.
FIG. 7 is a view for explaining the calibration of a conventional electron gun. In FIG. 7, in a scanning beam apparatus 21, an electron gun 22 irradiates an electron beam to a sample 30. A secondary beam or the like emitted from the sample 30 is detected by a detector 25, and a detecting device 26 obtains a detected signal. The calibration of the electron gun 22 is carried out by observing a grid image of a grid 23 disposed on the sample 30 or by measuring a filament current and emission current obtained from the electron gun 22, or an irradiated beam current.
Patent Document 2 has disclosed a calibration method by measuring an emission current, and Patent Document 3 has disclosed a calibration method by measuring a beam current.
Patent Document 1: Japanese Patent Publication (Kokai) No. 01-292736
Patent Document 2: Japanese Patent Publication (Kokai) No. 2001-150468
Patent Document 3: Japanese Patent Publication (Kokai) No. 2003-36807
In the conventional method of calibrating the electron gun, only the grid image is observed, or only the electric current relating to the electron gun is measured, and a relationship with respect to an object to be measured is not obtained. Accordingly, when the conventional method of calibrating the electron gun is applied to the scanning beam apparatus, while the electron gun can be calibrated, the detected signal strength is not calibrated.
Especially, the TFT array inspection apparatus inspects a defect in a base plate of a TFT array based on the potential strength on the base plate. Accordingly, even if the conventional technique of calibrating the electron gun is employed, it is difficult to calibrate the detected signal strength to obtain the potential strength on the base plate.
In view of the problems described above, the present invention has been made, and an object of the invention is to provide a TFT array inspection apparatus capable of calibrating detected signal strength to obtain potential strength on a base plate.
Further objects and advantages of the invention will be apparent from the following description of the invention.